Why Morning Sickness Might Actually Be Good For Moms And Babies

For many expectant mothers, the first months of pregnancy bring more than joy-they also bring waves of nausea, food aversions, and sometimes vomiting. Up to 80% of women experience morning sickness, and while it's often dismissed as just an unpleasant side effect, new research suggests it may actually serve an important purpose.

A team of UCLA researchers has found that morning sickness symptoms are tied to the body's immune system response during early pregnancy. Rather than being a sign something is wrong, these reactions may actually reflect a healthy process that helps protect both the mother and the developing baby.

Why the Body Reacts This Way

During pregnancy, a mother's immune system faces a tricky challenge: it must defend against infections without mistakenly attacking the fetus-which is half“foreign” because it carries genes from the father. To maintain this balance, the immune system adjusts its inflammatory signals while the body develops behavioral defenses like nausea and food aversions.

“These unpleasant symptoms are likely the body's way of keeping the pregnancy safe,” explains Professor Molly Fox, an anthropologist at UCLA and lead author of the study.

The study, published in Evolution, Medicine and Public Health, found that women with stronger inflammatory immune responses were more likely to report nausea, vomiting, or food aversions-particularly to substances like tobacco smoke or meat, which could carry pathogens.

An Evolutionary Safety Net

From an evolutionary perspective, morning sickness may have developed as a biological defense mechanism. By steering mothers away from risky foods and smells during the baby's most vulnerable early stages, the body reduces the chance of harmful exposure.

“Think of it as nature's built-in warning label,” says co-author Professor Daniel Fessler.“Just like packaging today tells pregnant women to avoid certain foods, morning sickness may have been evolution's original safeguard.”

More Than Just Biology

Beyond shedding light on human evolution, the findings could also help reduce stigma for pregnant women in workplaces. Recognizing morning sickness as a normal, biologically protective response could encourage better accommodations and support.

The UCLA team followed 58 Latina women in Southern California, measuring immune system markers called cytokines and linking them to reported pregnancy symptoms. They found a clear pattern: women with stronger pro-inflammatory responses reported higher levels of nausea, vomiting, and food aversions.

What's Next?

While the research strengthens the evolutionary theory behind morning sickness, the team cautions that more work is needed to confirm exactly how these immune and behavioral responses interact. Future studies could even help clinicians develop better ways to monitor pregnancy health without invasive testing.

For now, the takeaway is simple: while morning sickness can feel miserable, it may also be a reassuring sign that pregnancy is progressing normally-and that the body is doing exactly what it needs to keep both mother and baby safe.

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